1) Field of the Invention
The present invention relates to the bearing structure for the drive mechanism, image reader and image forming device equipped with the image reader.
2) Description of the Related Art
An image reader that scans a surface of a paper (copy surface) and outputs (prints) an image of the copy surface as image data is widely known. In such image readers, a luminous source or a mirror is mounted on the moving body which freely carries out linear reciprocating motion under the contact glass. The light from the illuminant light source is directed on to the copy surface for illuminating it while the moving body is shifted in the secondary (sub) scanning direction along the copy surface mounted onto the contact glass. The light reflected from the copy surface, for every line in the main scanning direction is focused on a charge coupled device (CCD) and made to form an image.
A stepping motor is used to move the moving body. The driving force of the stepping motor is transmitted to a wire pulley (or a gear) provided on a drive shaft. A wire fixed to the moving body is wound around the wire pulley. Thus, when the stepping motor is driven, the moving body performs the reciprocating motion.
In the conventional image forming device, the drive shaft is such that the wire pulley is fixed to one end whereas the other end is inserted into the bearing fitted in a frame of the image forming device.
FIG. 10 shows a schematic longitudinal side view of the bearing section 200 into which the other end of the driveshaft 300 is inserted. The bearing section 200 is composed of bearing hole 201 and bearing 202. The bearing hole 201 is made by cutting a notch in the frame 301 of the image reader. The bearing 202 has a flange 202b on one end of the bearing main body 202a. This flange 202b is made cylindrical in shape to enable the insertion of the drive shaft 300. The bearing section 200 is formed by inserting the bearing main body 202a of the bearing 202 into the bearing hole 201 and pressing the flange 202b against the frame body 301, thereafter, the drive shaft 300 is inserted into the bearing main body 202a of the bearing 202.
However the bearing section 200 has following problems. For example, if the gap between the bearing hole 201 and the bearing 202 is larger as shown in FIG. 11(a), the drive shaft 300 rattles in axial direction (i.e., X-axis) and radial direction (i.e., Y-axis). This rattle of the drive shaft 300 causes impulsive sound at the time of start up and stop as well as noise during the normal running due to the load while driving.
If the bearing 202 is press-fitted with respect to the bearing hole 201 as shown in FIG. 11(b), the bearing 202 might get tilted with respect to the bearing hole 201. If the bearing 202 gets tilted then the desired positioning accuracy of the bearing 202 with respect to the drive shaft 300 can not be achieved. If the bearing 202 can not be positioned accurately with respect to the drive shaft 300, a load is exerted on the drive shaft 300 resulting in lower driving efficiency (driving performance decrement) and lesser durability.